What do hippoboscids do to hawks?

Hippoboscids, commonly known as louse flies, are parasitic insects that primarily prey on birds, including hawks. These flies can have a detrimental effect on their hosts by sucking blood, which can lead to a range of health issues. One significant concern is the transmission of diseases; hippoboscids are known vectors for pathogens that can cause various infections in birds. Additionally, their blood-feeding behavior can lead to anemia, a condition where there is a deficiency of red blood cells or hemoglobin in the blood, causing weakness and fatigue in the affected birds.

In contrast, the other options suggest roles that hippoboscids do not fulfill. They do not help in grooming or provide any beneficial effects, and they certainly are not harmless. Rather, their impact is primarily negative, posing significant health risks to hawks and other birds they infest. Thus, acknowledging their role in disease transmission and potential to cause anemia accurately reflects the negative consequences these parasites have on hawks.